The Institute of Neurobiology of the Medical Sciences Campus of the University of Puerto Rico is an interdisciplinary, interdepartmental research facility devoted to the study of the structure and function of the nervous system with an emphasis on comparative cellular studies. It offers investigators and students from Puerto Rico, the rest of the United States and the Americas, as well as Europe, access to specimens of the rich Caribbean marine, terrestrial and fresh water fauna to be used as experimental models for neurobiological investigations. The studies are aimed at shedding light on cellular processes which must be understood to provide a rational basis for the diagnosis and treatment of a variety of neurological diseases. The Institute has collecting and holding facilities as well as the services of informed local naturalists. It acts as a focus around which a growing number of researchers interested in the various aspects of the neurosciences is reaching the critical mass necessary for productive interactions and the growth of collaborative efforts. The purpose of this program project grant is to provide funds, which, in addition to those provided by the Commonwealth of Puerto Rico, will support the general core activities (Histology, Zoology, Communication and Support Services) as well as many of the research efforts of the permanent faculty at the Institute. The present projects are: I. Development of synapses between identified neurons (Blagburn). II. Regulation and axonal transport of Na,K-ATPase (Corey-Specht). III. Neural control of the sea urchin spine ligament (del Castillo). IV. Anatomical basis of color vision in ground squirrels (Lugo-Garcia) V. Long-term interactions of neurons and glia (Orkand). VI. Modulation of crustacean muscle (Zuazaga).